Duct heater assembly



Aug. 27, 1963 R. 1.. BOYD ETAL DUCT HEATER ASSEMBLY 3 Sheets-Sheet 1 Filed March 31, 1960 INVENTOR.

R08RT L. BOYD J06 F. V01 Afl? Aug. 27, 1963 R. 1.. BOYD ETAL DUCT HEATER ASSEMBLY 3 Sheets-Sheet 2 Filed March 31, 1960 I ENIOR. R08R7 A. 07 J01? Fl V016??? Aug. 27, 1963 R. 1.. BQYD ETAL DUCT HEATER ASSEMBLY 5 Sheets-Sheet 5 Filed March 31, 1960 INVENTOR. #08597 L. 80V0 United States Patent 3,102,185 DUCT HEATER ASSEMBLY Robert L. Boyd and John F. Volker, Pittsburgh, Pa, assignors to Edwin L. Wiegand Company, Pittsburgh,

Filed Mar. 31, 1960, filer. No. 18,979 4 Claims. ((11. 21934) sembly and assembly is frequently essential, to minimize.

down time, when the assembly requires inspection and/ or replacement or repair of inoperative parts. Such difficulty has been especially prevalent where the heater assembly is relatively large and heavy. I

Another disadvantage of prior art heater assemblies has been that owing to the placement of the sensing unit of the usual thermal cut-out switch, improper operation of such switch would occur unless the assembly was properly installed in the duct with respect to the direction of fluid flow therethrough. Furthermore, when prior art assemblies are installed in ducts through which the fluid moves vertically rather than horizontally, switch operation is seldom satisfactory because an additional factor; i.e., convective-induced fluid flow, comes into being. Thus, when the normal direction of fan-forced fluid movement through the duct is opposite to conductive-induced fluid movement, prior art sensing unit placement results in wholly unsatisfactory operation of the thermal cut-off switch.

The present invention eliminates the difficulties attendant with prior art assemblies and these advantages, to gether with others possessed by the present invention, will readily become apparent from a study of the following description and from the appended drawings.

In the drawings accompanying this specification and forming a part of this application there is shown, for purpose of illustration, an embodiment which the invention may assume, and in these drawings:

FIGURE 1 is a fragmentary perspective view of a duct in which a heater of the present design is installed,

FIGURE 2 is an enlarged sectional view generally corresponding to the line 22 of FIGURE 1,

FIGURE 3 is a further enlarged sectional view generally corresponding to the line 33 of FIGURE 2 and having portions on the near side broken away to better illustrate the underlying structure,

FIGURE 4 is a broken sectional view generally corresponding to the line 44 of FIGURE 3,

This

3,12,185 Patented Aug. 27, 1963 2 only and that ducts having other cross-sectional configurations are contemplated.

In the present embodiment, duct 11 is divided transversely into longitudinally spaced duct portions 111, 211 between which the heater assembly is interposed. As best seen in FIGURES .2 and 3, the adjoining ends of respective duct portions 111, 2111 provide outwardly turned flange portions 12 which are adapted to be secured to respective sides of the heater assembly as will later appear.

Turning now to the heater assembly and with particular reference to FIGURE 2, such assembly comprises a U- shaped frame formed of a pair of side members 13 in spaced, side-byside, generally parallel relation connected together at one end by a cross-member 14. Such members are adapted to be welded or otherwise secured together to form a rigid assembly. URES 3 and 4, both the side members '13 and the crossmember 14 are presently channel-shaped in cross-section with their respective web portions 113, 114 directed inwardly to form, in effect, a continuation of the duct. Means are provided for closing the open end of the U- shaped frame aforesaid, such means comprising (see FIG- URE 4) a channel-shapedbase member 15 also arranged with its web portion 115 directed inwardly. Base member 15 may be removably secured to the frame side members 1 3 in any suitable manner and is seen in FIGURE 2, a fastening screw 16 may pass through an aperture in the web at one end of the member 15 and be threaded into a plate 1'7 which is welded or otherwise secured across the lower end of the adjoining side member 13. The opposite end of the base member 15' will, of course, be similarly secured to the other side member 13. For a purpose to appear, each end of base member 15 is closed by a plate 18, only one of which may be seen in FIGURE 2, while the flange portions of such member are spanned by a cover plate v19 removably secured in position by screws '20.

Carried by the web portion .115 of the base member 15 for disposition within the frame provided by the members 13, 14 are a plurality of electric resistance heating elements 21. As herein disclosed, each element is of the Well-known type wherein a resistor conductor is disposed within an elongated tubular metallic sheath filled with electric-insulating, heat-conductive material. The resistor conductor preferably terminates short of the sheath ends and has its ends connected to respective terminal pins 22 which project beyond respective sheath ends to provide for making electrical connections thereto.

With particular reference to FIGURE 4, each element 21 is formed to a hair pin configuration to provide a bight FIGURE 5 is a View similar to FIGURE 2 but showing certain parts separated to facilitate inspection and/or repair, and r FIGURE 6 is a perspective view of a detail.

With reference to FIGURE 1, the present invention comprises a heater assembly '10 which is adapted to be installed intermediate the ends of a duct 11 which, as herein illustrated, extends horizontally. A suitable fluid,

such as air, is adapted to flow through duct 11 to be heated by the heater assembly and, in so far as. the present invention is concerned, it is immaterial in which direction the air moves through the duct. In most cases, a suitable blower device (not shown) will be employed to move the air through the duct. While the present duct is herein shown to be generally square in cross-section, it is to be understood that such configuration is illustrative portion 2-3 and spaced-apart, generally parallel leg portions 24-. Also, in order to improve the heat-transfer characteristics of the element, the intermediate, heat-generating portion of each is provided with a spiral fin 2 5 which may be furnace brazed to the exterior of the element sheath. For a purpose to appear, a mounting plate 26 extends between and connects the legs 24 of each element adjacent its sheath ends and such plates may also be brazed to respective elements to form an integrated structure therewith.

As best seen in FIGURES 3 and 4, the elements 21 are adapted to be secured to the base member web 115 in spaced relation longitudinally of the member and with one of the legs of each element adjacent one side of the member and with the other leg of each element adjacent the other side of the member. The element legs are thus arranged in'two rows spaced longitudinally of the direction of :air movement through the duct. In order to obtain optimum heating efficiency, the elements will be slightly skewed (FIGURE 3) so that one element leg will not be disposed directly behind another where it As best seen in FIG- 1 would be exposed to "air already heated by the element leg in front of it. With the elements thus skewed, each element leg will have substantially equal exposure to unheated air flowing through the duct.

Turning now to the means for securing the elements to the base member 15, the web portion of the latter is apertured at 27 to pass respective element legs. Screws 28 extend through apertures in such member web portion and are threaded into respective mounting plates 26 to thus draw the latter tightly against the top (in the position of parts shown) of the base member web portion. From the foregoing, it willbe apparent that individual removal of the heating elements from the base member may readily be accomplished merely by removing the appropriate screws 28.

Difficulty is sometimes experienced in disassembling and assembling base member 15 with the frame structure formed by the members 13, 14 once the frame structure has been assembled with the duct. This is particularly true when the assembly is located in a rather inaccessible position or is disposed in a vertically extending duct rather 7 than a horizontal-1y extending one as herein illustrated.

The difliculty is, of course, aggravated when the assembly is relatively large and heavy.

To alleviate this difiiculty and as best seen in FIGURE 3, side members 13 provide respective guide channels 29 in opposed,,facin'g relation. Each guide channel 29 is generally U-shaped in cross-section and each extends longitudinally of its memlber 13 from the free end thereof. At the present time, guide channels 2 9 are spot welded to respective side members 13; however, other suitable means could as well be employed or such channels could be formed integrally with respective members if desired. Each guide channel 29 is adapted to slidably receive a respective end of a slide bar 30 secured to the heating elements 21 in the following manner.

As best seen in FIGURES 3 and 4, a sheet metal brace 31 extends between respective legs 24 of eachelement adjacent the latters bight portion 23., Referring now to FIGURE 6, each brace preferably comprises a length of sheet metal having a pair of slots 3'2, 33 at each end thereof entering from one side of the brace and providing at each brace end a pair of tabs 34, 35. Each slot 32 is of a size to accommodate the heating element sheath and the spacing between such slots corresponds to the spacing between respective legs of each element. Projecting transversely of an intermediate portion of each brace 31 is a tongue which is bent back upon the brace to provide a portion 36 which underlies the latter. For a purpose to appear, the free end of tongue portion 36 is apertured at 37.

Each brace 31 is adapted to be secured to a respective heating element 21 adjacent the latters bight portion 23 by disposing a respective element leg in respective brace slots 32. Brace tabs 34, 35 will then be bent toward each other to at least partially encircle la respective element leg to thus secure the brace in place. It is to be undersood that the spiral fin 25 will not interfere with bending of the tabs '34, 35' since each may be bent to coextend with the adjoining fin. It is also to be understood that the braces are so secured to respective heating elements that the brace tongue portions 36 are aligned with each other.

As best seen in FIGURE 4, the aforesaid slide bar 30 is disposed beneath (in the position of parts shown) the braces 31 for abutment with the brace tongue portions 36. Suitable screws 38 pass through the tongue portion apertures 37 (and are threaded into the slide bar to secure the latter to the braces.

It is common practice with heating assemblies of the general type herein disclosed to utilize a thermally responsive switch which will dc-energize the heating elely responsive switch aforesaid with respect to the heating.

elements is an important feature of the present invention. In the present embodiment, such heat sensing switch portion-comprises a bulb connected to the switch by means of a capillarytube; however, switches having other types of heat sensing elements could as well be employed.

In the present embodiment and as best seen in FIGURE 4, an elongated heat sensing bulb 39 is disposed intermediate the legs of respective heatingelements and extends transversely thereof. As herein shown, such bulb is presently located centrally of the bight portions of the elements. A capillary tube 40* (FIGURE 2) extends from the bulb to the switch. With the bulb thus positioned between the element legs of respective elements, it will be understood that the thermally responsive switch will operate in the same manner whether the air flows past the elements from left to right or right to left. It will readily be apparent that if the bulb 39 were positioned to one side or the other of the heating elements, a marked difference in switch operation would result between air fiow in one direction and airflow in the op posite direction.

With bulb 39 disposed as herein disclose-d, it will be exposed to radiant heat from several different directions. Since such exposure could cause premature switch operation, the sensing bulb is disposed within a tubular housing 41 which serves to interrupt the radiant heat. Housing 41 preferably has opposed, longitudinally extendingrib 42 may be secured by means of a screw 47.

Although not shown, it will be understood that the usual power leads may enter the base channel member 15 through an aperture formed therein for connection to the terminal pins of respective heating elements.

Assuming that the heater assembly 10 is secured to the duct 11 by means of screws 48 which extend through apertures in respective duct section flange portions 12 and are threaded into respective adjoining portions of the heater assembly members 13, 14 and 15, the heater assembly may be dismantled for inspection or replacement of parts as follows: In the event access to the interior of the base member 15 is desired, cover plate 19 may readily be removed by removing the screws 20. In the event further dismantling is necessary, those duct screws 48 which are threaded into the base member 15 will be removed. Next, the screws 16 will be removed and the base member 15 shifted downwardly to withdraw the heating elements from within the frame structure provided by the side members 13 and the cross member 14. As the base member is moved downwardly, slide bar 30 will slide along the guide channels 29 as will be evident.

Upon removal of the base member 15 as seen in FIGURE 5, replacement of any. of the heating elements will readily be effectuated by removing the slide bar 30, disconnecting the lead wires (not shown) from the appropriate element terminal pins, and removing the brackets 43 to respective braces 31 prior to separating the element from the basemember.

Assuming that the parts are disposed as illustrated in FIGURE 5 and that the base member-element subassembly is to be re-assembled with the frame provided by the side members 13 and the cross member 14, assembly will proceed as follows: The bight portion ends of the heating elements will be inserted between the frame side members until the ends of the slide bar 30 enter respective guide channels 29. The base member and element sub-assembly will then be shifted upwardly (in the position of parts shown) until the base member abuts the ends of respective side members. The screws 16 will then be installed to retain the parts assembled. If the electrical power leads (not shown) have been disconnected, they will be connected once again and the cover plate installed. Installation of the screws 4-8 through the duct flanges 12 and into the base member will complete the assembly operation.

It will readily be apparent that once the slide bar has'been inserted within the guide channels, the base member-element sub-assembly will easily slide to position, in much the same manner as a drawer is closed, with no juggling being required to keep the parts in alignment. It will also be apparent that the guidance and support provided by the slide bar-guide channel construction will be particularly advantageous in the event the assembly is mounted in a vertically extending duct rather than the horizontally extending one herein disclosed. This is so because the unbalanced condition created by the heavy heating elements being secured to one side of the base member makes installation of the base member-element sub-assembly difiicult to handle, especially in the larger heater assembly sizes.

While the base member of the present unit has been shown as being installed from the bottom of a horizontally extending duct, it will be understood that the parts could as well be arranged to assemble the base member from either side or from the top.

In view of the foregoing it will be apparent to those skilled in the art that we have accomplished at least the principal object of our invention and it will also be apparent to those skilled in the art that the embodiment herein described may be variously changed and modified, without departing from the spirit of the invention, and that the invention is capable of uses and has advantages not herein specifically described; hence it will be appreciated that the herein disclosed embodiment is illustrative only, and that our invention is not limited thereto.

We claim: 1

1. An electric heating assembly for use in a duct work system, comprising a housing adapted to be mounted within the duct work system whereby air flowing through the system enters said housing at one place and exhausts from said housing at a spaced place, a'plurality of hair-pin type electric heating elements mounted within said housing, each having a pair of legs extending transversely to the line of air flow therethrough, and thermal cut-out means for interrupting flow of electrical energy to said heating elements when a predetermined temperature is reached in said housing, said cut-out means including a heat sensing element located between opposed sides of the legs of at least certain of said hair-pin heating elements.

2. The construction according to claim 1 wherein said hair-pin type heaters extend cross-wise of the line of air flow, the legs of each heater being spaced along the line of air flow, and wherein said sensing element is elongated and extends longitudinally through the opening defined by the bight of at least certain of said heaters.

3. The construction of claim 2 wherein the legs of said heaters are rigidly connected to a member which covers a side opening in said housing and is removably connected thereto.

4. An electric heating assembly for use in a duct work system, comprising a rectangular box-like sheet metal housing having opposite open ends whereby air flowing in said system enters one end, passes through said housing and exhausts from the opposite end, each side of said housing being channel-shaped with the channel turned outwardly of the housing to provide spaced flanges around said housing for connection to spaced flanges extending from adjoining portions of said duct work system, one

extending transversely through said one side and each leg being of a length so that the bight of the respective element is disposed adjacent to that side wall which is opposite .to said one sidewall, a cross member connected to and extending cross-wise of said heating elements at a point spaced from said one side and in a direction inward of said housing, said cross-member bracing that part of the heating elements spaced from said one side and having opposed guide portions extending beyond said elements on each side thereof, said two adjoining sides each having spaced guide slides extending parallel to the direction of insertion movement of said heating elements and closely and slidably embracing the same to facilitate assembly movement of said one side and its supported elements with said housing, thermal cut-out means for interrupting flow of electrical energy to said heating elements and including an elongated heat sensing tube which extends through the opening formed by the bight of at least certain of said heating elements,

References Cited in the file of this patent UNITED STATES PATENTS 1,636,369 Johnson July 19, 1927 1,829,765 Spalding Nov. 3, 1931 1,841,361 Bulkeley Jan. 19, 1932 2,568,278 Favot Sept. 18, 1951 2,712,588 Epstein July 5, 1955 2,839,659 Cotts et al. June 17, 1958 2,893,639 Martin July 7, 1959 2,971,076 Ferguson Feb. 7, 1961 

1. AN ELECTRIC HEATING ASSEMBLY FOR USE IN A DUCT WORK SYSTEM, COMPRISING A HOUSING ADAPTED TO BE MOUNTED WITHIN THE DUCT WORK SYSTEM WHEREBY AIR FLOWING THROUGH THE SYSTEM ENTERS SAID HOUSING AT ONE PLACE AND EXHAUSTS FROM SAID HOUSING AT A SPACED PLACE, A PLURALITY OF HAIR-PIN TYPE ELECTRIC HEATING ELEMENTS MOUNTED WITHIN SAID HOUSING, EACH HAVING A PAIR OF LEGS EXTENDING TRANSVERSELY TO THE LINE OF AIR FLOW THERETHROUGH, AND THERMAL CUT-OUT MEANS FOR INTERRUPTING FLOW OF ELECTRICAL ENERGY TO SAID HEATING ELEMENTS WHEN A PREDETERMINED TEMPERATURE IS REACHED IN SAID HOUSING, SAID CUT-OUT MEANS INCLUDING A HEAT SENSING ELEMENT LOCATED BETWEEN OPPOSED SIDES OF THE LEGS OF AT LEAST CERTAIN OF SAID HAIR-PIN HEATING ELEMENTS. 